# voltage of collector and base?

Discussion in 'Homework Help' started by no12thward, Jan 23, 2011.

1. ### no12thward Thread Starter Member

Jan 10, 2011
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how do I go about finding the VOLTAGE of the Collector(Vc) and the Base(Vb) in this collector feedback circuit? Ive found Current of collector(Ic), Emitter(Ie), and Base(Ib). But do I have to account for the 10V Vcc at the top when finding Vc and Vb (before applying Ohms Law)?

Thanks guys!!!!

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2. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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The current at the emitter is Ic+Ib.

To find the voltage at collector, multiply collector current by collector resistor, subtract from 10V.

To find emitter voltage, multiply emitter current by emitter resistance value.

Base voltage is found with the current through the bias resistor. It is typically 0.6 or 0.7V, to help verify your calculations.

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3. ### no12thward Thread Starter Member

Jan 10, 2011
30
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"The current at the emitter is Ic+Ib."

Even for a collector feedback circuit? I thought Current at the emitter would be (Beta+1)(Ic)? Is that not right?

4. ### Ron H AAC Fanatic!

Apr 14, 2005
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I think you have to assume a value for Vbe (0.6-0.7V) in order to solve for the operating point.

5. ### Ron H AAC Fanatic!

Apr 14, 2005
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But Ib=Ic/beta. Do a little algebra, and you'll see that both are correct.

6. ### no12thward Thread Starter Member

Jan 10, 2011
30
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silly me! you guys are right. Thanks! So my Vce would be somewhere around 4.8V if Ive done my calcs. correct

7. ### Ron H AAC Fanatic!

Apr 14, 2005
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Looks good to me.

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8. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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The way I read the OP was that he already had the currents, so the operating point was known (somewhat). If he had zero info, then a SWAG vbe is needed.

9. ### Ron H AAC Fanatic!

Apr 14, 2005
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659
Well, he did say he had found the currents. I missed that. Of course, to find them (unless he found them in a book), he had to know Vbe.
His question was really about using Vcc in solving for node voltages (I think).